The present invention relates, in general, to a test apparatus, and more particularly, to movement of a portion of the test apparatus.
Generally, integrated devices are fabricated in a thin flat substrate material commonly referred to as a semiconductor wafer. After fabrication, the integrated devices in the semiconductor wafer are tested, the semiconductor wafer is separated or divided into individual semiconductor chips or die, and each chip is encapsulated in a package. Since each semiconductor chip typically contains a large number of integrated devices, there is a probability of producing one or more defective integrated devices. Therefore, it is desirable to test the integrated devices prior to packaging them to ensure that time, money, and manufacturing capacity are not wasted by packaging defective semiconductor chips. Moreover, testing semiconductor chips in wafer form is easier and more cost efficient than testing a single semiconductor chip that has been separated from the semiconductor wafer. In other words, wafer-level testing or probing, i.e., testing semiconductor chips before the semiconductor wafer is separated into individual chips, reduces the manufacturing costs and cycle times associated with manufacturing semiconductor products.
An important step in wafer-level testing is electrically contacting electrode pads on a semiconductor wafer with corresponding probe-card probes or wire-probes on a probe card. Failure of any of the probe-card probes to make electrical contact with a corresponding electrode pad may preclude testing the semiconductor chip or produce erroneous test results. Typically, a prober is programmed to position the semiconductor wafer so the electrode pads on the wafer electrically contact the probe-card probes. Factors that may prevent adequate electrical contact include variations in wafer-to-wafer thickness, variations in thickness within a wafer, and hardened contact bumps on the electrode pads that cause the probe-card probes to slide off the contact bumps.
One technique to ensure electrical contact between a probe-card probe and an electrode pad employs a capacitive or pneumatic sensor to sense the distance between the semiconductor wafer surface and the probe-card probes. The sensor adjusts the semiconductor wafer so the electrode pads on the wafer contact the probe-card probes. A drawback of this technique is that for large variations in the height of the electrode pads, the time required to adjust the semiconductor wafer is long. Another technique employs a mechanical switch that contacts a scribe grid on the wafer. Again, there may be a large variation in the heights of the contact pads which would require time consuming adjustments of the wafer.
Accordingly, it would be advantageous to have a method and a means for controlling a position of a semiconductor wafer in accordance with the heights of conductive pads on the wafer. It would be of further advantage for the method to include a fail-safe system to prevent the probe card or semiconductor wafer from becoming damaged.